Inheritance Flashcards
What is a gene?
-A sequence of DNA bases (arranged as triplets) that codes for a particular polypeptide (each triplet codes for one specific polypeptide chain)
What are two characteristics that genes (alleles) have?
-can separate and combine (during sexual reproduction/fertilisation)
- can mutate (change DNA base sequence)
What are homologous pairs of chromosomes?
A homologous pair of chromosomes consists of two chromosomes, one from each parent, that are similar in size, shape, and genetic content, carrying genes for the same traits.
What are alleles?
alternative forms of genes occupying the same gene position (or locus) on homologous chromosomes
what are the three different (theoretical) allele combinations for any single gene?
Heterozygous, homozygous, dominant, homozygous recessive
In homologous chromosomes, where is each chromosome originated from?
- one originated from the egg
- one originated from the sperm
What do alleles of the same gene do?
occupy the same locus
what is heterozygous?
Having different alleles for a given gene (where a dominant allele and a recessive allele are present together). Each allele is carried on a different chromosome within a pair of homologous chromosomes. E.g. Bb
What is homozygous dominant?
Having the same two dominant alleles present for a given gene. Each allele is carried on a different chromosome within a pair of homologous chromosomes. E.g. BB
What is homozygous recessive?
Having the same two recessive alleles present for a given gene. Each allele is carried on a different chromosome within a pair of homologous chromosomes. E.g. bb
What is the gene pool?
All the alleles in a population at any one time
How is a dominant allele expressed?
always expressed in the phenotype (physical appearance of the organism)
How is a recessive allele expressed?
only expressed in the phenotype (physical appearance of the organism) when no dominant allele is present
What is definition of genotype?
-The genetic make up of an individual; all of the alleles that they possess
-These alleles dictate their observable characteristics (phenotype)
what is the definition of phenotype?
The observable characteristics of an organism determined by the genotype
What is a particular characteristic controlled by and what does this mean? (genotype and phenotype)
a particular characteristic is controlled by a single gene therefore if an organism is homozygous dominant or heterozygous for a particular characteristic, the dominant allele will always be expressed in the phenotype
What happens when a homozygous dominant flower with purple petals is crossed with a homozygous recessive flower with white petals?
each gamete from each flower provides one allele to the offspring
What does mono hybrid mean?
one gene
what is a test cross?
used to determine an unknown genotype when the dominant phenotype is present (cross unknown phenotypically dominant plant with homozygous recessive plant and look at offspring: Are they dominant or a one-to-one ratio of homozygous, dominant and homozygous recessive phenotypes?)
What is monohybrid inheritance?
The inheritance of a single gene such as that controlling plant height or seed colour
What did mendel investigate?
Inheritance in plants of the garden pea
Why were the plants a useful choice for inheritance experiments?
•Easy to grow / large numbers of offspring quickly
•Can self or cross fertilise
•Produce flower and fruit in the same year (see phenotypes quickly)
What did Mendel do and what did he find?
-chose pairs of conntrasting characteristics such as tall or dwarf plants, Round or wrinkled seeds and yellow and green seeds
-He was fortunate that his choice of characteristics were controlled by single gene, and were easy to tell apart
What are three characteristics of a gene?
•Has a sequence of codons that specifies the sequence of amino acids in a polypeptide chain
•Genes can separate and combine (during sexual reproduction)
•Genes can mutate (change DNA sequence